1. Field of the Invention
This invention relates generally to control devices for turbochargers, and more particularly to an improved turbocharger control device for use in conjunction with internal combustion engines.
2. Prior Art of the Invention
Turbochargers generally are installed in engines for improving the output power of the engine by increasing the air flow charge to the cylinders to support an increased fuel charge. Because the power delivered by the engine can be drastically increased if the air flow to the engine is increased excessively, it is necessary to prevent the increased output power from exceeding a critical level and having a detrimental influence on the integrity of the engine. In order to prevent this influence, there has been proposed a control system which operates to prevent the air charge from exceeding a safe level in view of the characteristics of the engine.
The above-mentioned conventional control system which is self-regulating detects the pressure of the air flow charge supplied to an engine intake manifold by the compressor component of a turbocharger, utilizes this air flow pressure to operate a control device which, in turn, controls the exhaust gas flow to the turbine component using a servomechanism.
Because the above-mentioned conventional control system senses the pressure of the air flow supplied from the compressor and operates the control device by means of detecting the air flow pressure, the turbine and compressor can reach an unacceptably high speed of rotation before the control device can operate to reduce exhaust gas flow to the turbine. This "overspeed" condition can result in increases in the air flow pressure over the maximum permissible levels before the compressor shaft speed can be slowed, especially during rapid increases in engine power. In order to compensate for compressor overspeed, the upper limit of the air flow pressure is conventionally set in a pressure range which is low relative to the maximum steady state air flow pressure capacity of the engine. Accordingly, it is difficult to make full use of the ability of the turbocharger with such conventional control systems and devices.
Furthermore, because the turbine rotates at comparatively high speeds and experiences high stress levels even at a time when its thermal environment (temperature of exhaust gases) corresponds to normal engine conditions, it is especially important that the rotation of the turbine not be inadvertently or unnecessarily increased under the harmful thermal environment caused by the higher temperatures of the exhaust gases at high power conditions, in order to maintain the strength and integrity of the turbine component of the turbocharger. Also, the construction of the control device should be relatively simple and compact. And, the control device should be constructed using components which retain strength and durability under the thermal environment caused by hot exhaust gases, so that the control device may operate precisely and exactly.